The research, by scientists from the National Institute on Alcohol Abuse and Alcoholism, also showed that three out of every 10 Americans who used marijuana in the past year were classified as having a marijuana use disorder, meaning abuse or dependence on the drug, which adds up to about 6.8 million Americans. Groups with notable increases in this category included those ages 45 to 64 and individuals who are black or Hispanic, with the lowest incomes or living in the South. However, the rate of people with marijuana use disorders has declined among marijuana users overall, from about 36 percent in 2001-2002 down to about 31 percent in 2012-2013.

"The trend upward in marijuana use indicates that more adults are at risk for marijuana-related adverse consequences, including the risk of marijuana use disorders (abuse or dependence) that we showed. Our findings are consistent with the studies of others that have shown increases in problems such cannabis-related emergency room visits and fatal vehicle crashes," the study's lead author, Deborah Hasin, a professor of epidemiology at Columbia University, told CBS News.

"I'm not too surprised by the results," said Dr. Larissa Mooney, an associate clinical professor of psychiatry and director of the UCLA Addiction Medicine Clinic, who was not involved with the research. "There's an increase in prevalence of marijuana use because it's become more and more available."

Typically, said Mooney, when any substance is made more available, its use is expected to go up.

Legalization also tends to change perceptions about risks associated with using the substance, Mooney said. "A greater number of people view marijuana as less risky. There are less perceived harms. I think we are tasked with really educating the public and our patients about the potential risks and harms associated with marijuana use. It's not without risk or potential harm," she said.

The authors wrote in their study, "As is the case with alcohol, many individuals can use marijuana without becoming addicted. However, the clear risk for marijuana use disorders among users (approximately 30 percent) suggests that as the number of U.S. users grows, so will the numbers of those experiencing problems related to such use. This information is important to convey in a balanced manner to health care professionals, policy makers and the public."

According the Substance Abuse and Mental Health Services Administration (SAMHSA), marijuana's immediate effects include distorted perception, difficulty with thinking and problem solving, and loss of motor coordination. Long-term use can contribute to respiratory infection, impaired memory, and exposure to cancer-causing compounds. Heavy marijuana use in youth has also been linked to an increased risk for developing mental illness and poorer brain health. Cannabis use disorder can lead a higher tolerance and cravings for it, as well as development of withdrawal symptoms such as the inability to sleep, restlessness, nervousness, anger, or depression.

Mooney told CBS News, "Some people use it recreationally and don't become addicted, but for a subset of users, marijuana can be addictive. There are many factors that contribute to someone's vulnerability. A family history of addiction, genetics, social factors have a role. Having a co-occurring psychiatric disorder or a history of trauma or abuse."

She said as more people use it, more will need treatment and help for problems related to marijuana use. "We'll need to have treatments and services available, substance use disorder treatment, like those we provide for alcohol users who are now addicted."

Study author Hasin added, "This is important information for individuals to consider when making personal choices about using marijuana, and for the public to have when considering legalization."